Remote Sensing of Fire and Smoke in Indonesia:
The Along Track Scanning Radiometer (ATSR) Fire Product of Indonesia
(IFFN No. 18 – January 1998, p. 30-32)
ATSR instrument characteristics
The Along Track Scanning Radiometer (ATSR), developed by a consortium of laboratories led by the Rutherford Appleton Laboratory, is flying on board the ERS satellites since 1991 (ESA 1992). The ATSR-2 (Stricker et al. 1995) which has been used for this monitoring, has four visible and near infrared channels centred at 0.55m m, 0.65 mm, 0.86m m and 1.6m m, together with the mid-infrared and thermal-infrared channels centred at 3.7m m, 10.8m m and 12 m m. The ATSR is an instrument with a conical scan system producing a double view (forward view: 55 degrees to the nadir) of the same surface at 1 km resolution. The 512 km swath allows a repetitive coverage over the area of interest with about 3 days revisiting frequency at equatorial latitude. The instrument is equipped with a very precise on-board calibration system and with the Stirling Cycle Cooler, which keeps the temperature of detectors within their optimum range thus ensuring an excellent accuracy of measurement. The ATSR high radiometric sensitivity, the good signal to noise (NEDT ~0.05 K, for mid and thermal infrared channels [Mason 1991]), together with the 12 bits digitisation enable the detection of fine ground structures. This is essential specifically for night time image analysis. The same instrument will fly on ENVISAT-1 to be launched at the end of 1999. This would ensure the continuity of the measurements.
At the request of the user community as well as for public information, a fast delivery service dedicated to fire monitoring application has been set up at ESRIN. The night time acquisitions of the ATSR-2 instrument on board ERS-2 are processed in order to visualize and localize hot spots in South East Asia. The results of the ERS-2 Indonesian fire survey are available from ESA WWW server, http://shark1.esrin.esa.it.
ATSR Data Flow and Products
The hot spots detection has been performed from August to November 1997. The ATSR data stream is recorded on board ERS and dumped at ESA stations. The exact ERS-2 orbit cycle of 35 days allows to revisit the same scene with the same geometrical condition, as well as a very precise localisation (Dow et al. 1996). Night time data have been processed by the SADIST processor into Gridded Brightness Temperature (GBT) product consisting of 512 x 512 km frame rectified in along track/across-track coordinates and gridded into 1 km cells (RAL 1995).
“Hot Spot” Detection with ATSR
During the night, in absence of reflected solar energy, the irradiance at 3.7m m, coming from the earth emission at 500 K is about two orders greater than the one from the earth surface at 300 K. At night and for the seasonal period observed, the average background temperature over the tropical area varies around 295K. Thus even with a fire partially filling a sub pixel surface, the 3.7m m channel of the ATSR will provide a sensitive signal (Dozier 1981). The ATSR instrument, designed initially for sea surface measurements (Mutlow et al. 1994), saturates at 312 K in channel 3.7m m. Therefore, for the rest of the paper, a hot spot will be identified each time the temperature at sensor level reaches this saturation. The high level radiometry quality of the ATSR (Mason 1991, Mutlow et al. 1994, Stricker et al. 1995), as well as the high quality orbit of ERS (Dow et al. 1996) allow it to get a high confidence in the detection and localisation of the hot spots.
Caveats and Recommendations
The images processed in this way preserve all the original details leaving the user the evaluation of hot features. The detected fires can be considered as highly likely, however some fires can be missed. The user of the fire product needs to take into account the algorithm limitations due to cloud presence, atmospheric effects, bi-directionality of emissivity, fire temperature and extension, which are not taken into account in the processing.
Advantages of ATSR
Night Time detection ensures that no algorithm problem is expected due to sunlight reflection. Only quasi nadir viewing pixels are analyzed: less pixel size and bi-directional problems are expected. No drift of the ERS orbit allows year to year comparison. High radiometric sensitivity allow it to pick up little/not extended fires.
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Dozier, J. 1981. A method for satellite identification of surface temperature fields of subpixel resolution. Remote Sensing of the Environment 11, 221-229.
Dow, J.M., M.Rosengren, X.Marc, R.Zandbergen, R.Piriz, and M.Romay Merino. 1995. Achieving, assessing and exploiting the ERS-1/2 Tandem Orbit Configuration, ESA Bulletin Numero 83, February 1996.
ESA. 1992. ERS-1 System, ESA SP-1146.
ESA. 1992. ERS-1 User Handbook, ESA SP-1148.
Mason, 1981: Satellite measurement of sea surface temperature. Doctorate Thesis, University of Oxford.
Mutlow, C.T., D.T.Llewellyn-Jones, A.M.Zavody, I.J.Barton. 1994. Sea surface temperature measurement by the Along Track Scanning Radiometer on the ERS-1 satellite: early result. J. Geophys. Res. 99, 22,575-22,588.
RAL, 1995: SADIST-2 v200 Products, P. Bailey ER-TN-RAL-AT-2164, Rutherford Appleton Laboratory. 6th September 1995 release.
Stricker, N.C.M., A.Hahne, D.L.Smith, J.Delderfield, M.B.Oliver, and T.Edwards. 1995. ATSR-2: The Evolution in its design from ERS-1 to ERS-2. ESA Bulletin No. 83 (August 1995).
Fig.1. 1 August to 28 November 1997 ATSR fire summary of Borneo (7456 saturated pixels for the whole period)
Fig.2. August 1997 ATSR fire summary of Indonesia (2042 saturated pixels on 39 frames)
Fig.3. September 1997 ATSR fire summary of Indonesia (5012 saturated pixels on 20 frames)
From: Olivier Arino, Alessandra Buongiorno,
and Eve Antikidis Address:
European Space Research Institute (ESRIN)
European Space Agency (ESA)
Via Galileo Galilei
I – 00044 Frascati